1. Field
The present invention relates to illumination optical apparatus, exposure apparatus, and device manufacturing methods and, more particularly, to an illumination optical apparatus suitable for an exposure apparatus for manufacturing such devices as semiconductor devices, imaging devices, liquid-crystal display devices, and thin-film magnetic heads by a lithography process.
2. Description of the Related Art
The photolithography process for manufacturing the semiconductor devices and others is carried out using an exposure apparatus for projecting a pattern image of a mask (or reticle) through a projection optical system onto a photosensitive substrate (a wafer, a glass plate, or the like coated with a photoresist) to effect an exposure thereof. The ordinary exposure apparatus is arranged to form a pattern of one kind in one shot area (unit exposure region) on the photosensitive substrate.
In contrast to it, a method proposed for improvement in throughput is a double exposure method of effecting exposures of patterns of two kinds in a superimposed state in one shot area on a photosensitive substrate to form one synthetic pattern (cf. Japanese Patent Application Laid-open No. 2000-21748).
The exposure apparatus of the double exposure method is arranged, for example, as follows: a first pattern region on the mask is illuminated to transfer a pattern in the first pattern region into one shot area on the photosensitive substrate, and thereafter a second pattern region on the mask is illuminated to transfer a pattern in the second pattern region into the same shot area on the photosensitive substrate. In order to improve the throughput of the exposure apparatus, it is necessary to quickly perform switching between polarization states of illumination light in the first pattern region and in the second pattern region according to characteristics of the patterns.